Problem: The sum of $6$ consecutive odd numbers is $84$. What is the third number in this sequence?
Explanation: Call the first number in the sequence $x$ The next odd number in the sequence is $x + 2$ The sum of the $6$ consecutive odd numbers is: $x+ (x + 2)+ (x + 4)+ (x + 6)+ (x + 8)+ (x + 10) = 84$ $6x + 30= 84$ $6x = 54$ $x = 9$ Since $x$ is the first number, $x + 4$ is the third odd number. Thus, the third number in the sequence is $13$.